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how much voltage at the coil???

Discussion in 'The Hokey Ass Message Board' started by FEDSLED, Nov 28, 2005.

    Joined: Jan 4, 2003
    Posts: 251

    from lynnweed

    How much voltage should be at the posotive side of the coil. I am running a gm style one wire alternator that puts out 14 volts while running and I got a ballast resistor in the wire that goes to the coil to bring it down to 12.4 volts. is that to much voltage at the coil. if so how do I reduce it.
    thanks FED
    Joined: May 23, 2005
    Posts: 4,407

    Alliance Vendor
    from AUSTIN,TX

    I think it was like 9 or 10 originally. I cut mine out and put in a dodge type...and I carry a spare bolted directly above it. I also gotta say I have seen them wired direct with no ballast resistor and they still seem to last a long time.
  3. No, that is not too much.
  4. Rocket Scientist Chris
    Joined: Mar 3, 2001
    Posts: 560

    Rocket Scientist Chris

    You can add another resistor to the circuit, but you'll have to do a little calculating (use Ohm's law) to find out how much more resistance will be needed to give the necessary 9 volts. But, that will only be 9 volts at the coil when the alternator is putting out the 14 volts. As the alternator charges the battery, the output voltage will drop and so will the voltage to the coil. The result is a less than optimum spark. The problem with running more than 9 volts to coil is the contacts tend to burn and shorten the life of the points.

    I ran into this very problem when I converted my '55 Mercury to 12 volts. The GM one-wire alternator I used actually put out closer to 15 volts. To get around the need for all the extra resistors, I just converted the points ignition to electronic using a Pertronix kit. :)

  5. Most systems, generator/or alternator are regulated at the top end somewhere in the 14 volt range, so the GM one-wire has'nt changed anything. One ballast resistor is enough.

  6. skipperman
    Joined: Dec 24, 2002
    Posts: 1,837


    Did you check coil voltage with the car RUNNING ? it should be LOWER with a load on it ......check into resistor and after resistor...It should be about 9V ...but a pertronix cures all the and a LOT more !!

    jersey skip

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